The TRIO.BAS™ instruments utilize the impaction method of air sampling. The air, passing through an aspirating head, impacts onto an appropriate agar plate that collects bacteria or other organic substances possibly present in the sampled area.
Per USP <797>, "Volumetric active air sampling of all classified areas using an impaction device must be conducted in each classified area [e.g., ISO Class 5 PEC and ISO Class 7 and 8 room(s)] during dynamic operating conditions at least every 6 months."